Forensic evidence doesn’t always tell the truth.

If only forensics were that reliable. Instead, to judge by the most comprehensive study on the reliability of forensic evidence to date, the error rate is more than 10% in five categories of analysis, including fiber, paint and body fluids. (Meaning: When the expert says specimen X matches source Y, there’s a 10% probability he’s wrong.) DNA and fingerprints are more reliable but still not foolproof. The 1995 study, in the Journal of Forensic Sciences, looked at proficiency tests labs take to see whether their work is sound.

More recent studies have also shown problems. Though a 2005 study in the Journal of Criminal Law & Criminology suggests a fingerprint false-positive rate a bit below 1%, a widely read 2006 experiment shows an alarming 4% false-positive rate.

Yet the public sees errors as gross anomalies. Like the time the FBI wrongly linked an Oregon attorney named Brandon Mayfield to the 2004 Madrid commuter train bombing that killed 200 people. The FBI had claimed a 100% match between fingerprints found at the scene and Mayfield, who was held for two weeks in federal custody. When the Spanish National Police got the real perpetrator, an Algerian named Ouhnane Daoud, the FBI had to admit its mistake. Mayfield accepted a $2 million settlement from the government.

Another debacle, this time involving DNA testing: Josiah Sutton served four and a half years for rape after the Houston Crime Lab tied him to crime-scene DNA. The lab was later found to be rife with problems, including a leaky roof that let rainwater contaminate evidence. Sutton was proclaimed innocent in 2004 and awarded $118,000 in reparations the next year.

Forensic evidence is also used in white-collar cases. In the Martha Stewart trial, government forensic scientist Larry F. Stewart (no relation to Martha) testified that he had performed incriminating tests on the famous “@60″ written next to “
ImClone
” on a worksheet used to record Martha Stewart’s securities positions. The notation suggested that she had a long-standing agreement to sell ImClone should the price hit $60, which would have cleared her of insider trading. Larry Stewart said his tests showed the potentially exonerating notation was made with different ink, thereby suggesting that it might have been added later.

When the court learned that someone else performed the tests he claimed to have done himself, Larry Stewart was tried for perjury. The tester had done an incomplete job, failing to compare the “@60″ ink to all the other ink on the page. (Larry Stewart was acquitted.)

How can we preserve the usefulness of forensic evidence while protecting the public when it breaks down? The core problem with the forensic system is monopoly. Once evidence goes to one lab, it is rarely examined by any other. That needs to change. Each jurisdiction should include several competing labs. Occasionally the same DNA evidence, for instance, could be sent to three different labs for analysis.

This procedure may seem like a waste. But such checks would save taxpayer money. Extra tests are inexpensive compared to the cost of error, including the cost of incarcerating the wrongfully convicted. A forthcoming study I wrote for the Independent Institute (a government-reform think tank) shows that independent triplicate fingerprint examinations in felony cases would not only eliminate most false convictions that result from fingerprint errors but also would reduce the cost of criminal justice if the false-positive error rate is more than 0.115%, or about one in a thousand.

Other reforms should include making labs independent of law enforcement and a requirement for blind testing. When crime labs are part of the police department, some forensic experts make mistakes out of an unconscious desire to help their “clients,” the police and prosecution. Independence and blind testing prevent that. Creating the right to a forensic expert for the defense would help restore the imbalance in scientific firepower that too often exists between prosecution and defense. Private labs are subject to civil liability claims and administrative fines, giving them financial incentives to get it right.

Roger Koppl is a professor of Economics and Finance at Fairleigh Dickinson University’s Silberman College of Business and a Director of the Institute for Forensic Science Administration.